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NAME

     sigvec — software signal facilities

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <signal.h>

     struct sigvec {
             void     (*sv_handler)();
             int      sv_mask;
             int      sv_flags;
     };

     int
     sigvec(int sig, struct sigvec *vec, struct sigvec *ovec);

DESCRIPTION

     This interface is made obsolete by sigaction(2).

     The system defines a set of signals that may be delivered to a process.  Signal delivery
     resembles the occurrence of a hardware interrupt: the signal is blocked from further
     occurrence, the current process context is saved, and a new one is built.  A process may
     specify a handler to which a signal is delivered, or specify that a signal is to be blocked
     or ignored.  A process may also specify that a default action is to be taken by the system
     when a signal occurs.  Normally, signal handlers execute on the current stack of the
     process.  This may be changed, on a per-handler basis, so that signals are taken on a
     special signal stack.

     All signals have the same priority.  Signal routines execute with the signal that caused
     their invocation blocked, but other signals may yet occur.  A global signal mask defines the
     set of signals currently blocked from delivery to a process.  The signal mask for a process
     is initialized from that of its parent (normally 0).  It may be changed with a sigblock(2)
     or sigsetmask(2) call, or when a signal is delivered to the process.

     When a signal condition arises for a process, the signal is added to a set of signals
     pending for the process.  If the signal is not currently blocked by the process then it is
     delivered to the process.  When a signal is delivered, the current state of the process is
     saved, a new signal mask is calculated (as described below), and the signal handler is
     invoked.  The call to the handler is arranged so that if the signal handling routine returns
     normally the process will resume execution in the context from before the signal's delivery.
     If the process wishes to resume in a different context, then it must arrange to restore the
     previous context itself.

     When a signal is delivered to a process a new signal mask is installed for the duration of
     the process' signal handler (or until a sigblock(2) or sigsetmask(2) call is made).  This
     mask is formed by taking the current signal mask, adding the signal to be delivered, and
     or'ing in the signal mask associated with the handler to be invoked.

     The sigvec() function assigns a handler for a specific signal.  If vec is non-zero, it
     specifies a handler routine and mask to be used when delivering the specified signal.
     Further, if the SV_ONSTACK bit is set in sv_flags, the system will deliver the signal to the
     process on a signal stack, specified with sigaltstack(2).  If ovec is non-zero, the previous
     handling information for the signal is returned to the user.

     The following is a list of all signals with names as in the include file <signal.h>:

     NAME            Default Action          Description
     SIGHUP          terminate process       terminal line hangup
     SIGINT          terminate process       interrupt program
     SIGQUIT         create core image       quit program
     SIGILL          create core image       illegal instruction
     SIGTRAP         create core image       trace trap
     SIGABRT         create core image       abort(3) call (formerly SIGIOT)
     SIGEMT          create core image       emulate instruction executed
     SIGFPE          create core image       floating-point exception
     SIGKILL         terminate process       kill program
     SIGBUS          create core image       bus error
     SIGSEGV         create core image       segmentation violation
     SIGSYS          create core image       non-existent system call invoked
     SIGPIPE         terminate process       write on a pipe with no reader
     SIGALRM         terminate process       real-time timer expired
     SIGTERM         terminate process       software termination signal
     SIGURG          discard signal          urgent condition present on socket
     SIGSTOP         stop process            stop (cannot be caught or ignored)
     SIGTSTP         stop process            stop signal generated from keyboard
     SIGCONT         discard signal          continue after stop
     SIGCHLD         discard signal          child status has changed
     SIGTTIN         stop process            background read attempted from control terminal
     SIGTTOU         stop process            background write attempted to control terminal
     SIGIO           discard signal          I/O is possible on a descriptor (see fcntl(2))
     SIGXCPU         terminate process       cpu time limit exceeded (see setrlimit(2))
     SIGXFSZ         terminate process       file size limit exceeded (see setrlimit(2))
     SIGVTALRM       terminate process       virtual time alarm (see setitimer(2))
     SIGPROF         terminate process       profiling timer alarm (see setitimer(2))
     SIGWINCH        discard signal          Window size change
     SIGINFO         discard signal          status request from keyboard
     SIGUSR1         terminate process       User defined signal 1
     SIGUSR2         terminate process       User defined signal 2

     Once a signal handler is installed, it remains installed until another sigvec() call is
     made, or an execve(2) is performed.  A signal-specific default action may be reset by
     setting sv_handler to SIG_DFL.  The defaults are process termination, possibly with core
     dump; no action; stopping the process; or continuing the process.  See the above signal list
     for each signal's default action.  If sv_handler is SIG_IGN current and pending instances of
     the signal are ignored and discarded.

     If a signal is caught during the system calls listed below, the call is normally restarted.
     The call can be forced to terminate prematurely with an EINTR error return by setting the
     SV_INTERRUPT bit in sv_flags.  The affected system calls include read(2), write(2),
     sendto(2), recvfrom(2), sendmsg(2) and recvmsg(2) on a communications channel or a slow
     device (such as a terminal, but not a regular file) and during a wait(2) or ioctl(2).
     However, calls that have already committed are not restarted, but instead return a partial
     success (for example, a short read count).

     After a fork(2) or vfork(2) all signals, the signal mask, the signal stack, and the
     restart/interrupt flags are inherited by the child.

     The execve(2) system call reinstates the default action for all signals which were caught
     and resets all signals to be caught on the user stack.  Ignored signals remain ignored; the
     signal mask remains the same; signals that interrupt system calls continue to do so.

NOTES

     The mask specified in vec is not allowed to block SIGKILL or SIGSTOP.  This is done silently
     by the system.

     The SV_INTERRUPT flag is not available in 4.2BSD, hence it should not be used if backward
     compatibility is needed.

RETURN VALUES

     The sigvec() function returns the value 0 if successful; otherwise the value -1 is returned
     and the global variable errno is set to indicate the error.

EXAMPLES

     On the VAX-11 The handler routine can be declared:

           void handler(sig, code, scp)
           int sig, code;
           struct sigcontext *scp;

     Here sig is the signal number, into which the hardware faults and traps are mapped as
     defined below.  The code argument is either a constant as given below or, for compatibility
     mode faults, the code provided by the hardware (Compatibility mode faults are distinguished
     from the other SIGILL traps by having PSL_CM set in the psl).  The scp argument is a pointer
     to the sigcontext structure (defined in <signal.h>), used to restore the context from before
     the signal.

ERRORS

     The sigvec() function will fail and no new signal handler will be installed if one of the
     following occurs:

     [EFAULT]           Either vec or ovec points to memory that is not a valid part of the
                        process address space.

     [EINVAL]           The sig argument is not a valid signal number.

     [EINVAL]           An attempt is made to ignore or supply a handler for SIGKILL or SIGSTOP.

SEE ALSO

     kill(1), kill(2), ptrace(2), sigaction(2), sigaltstack(2), sigblock(2), sigpause(2),
     sigprocmask(2), sigsetmask(2), sigsuspend(2), setjmp(3), siginterrupt(3), signal(3),
     sigsetops(3), tty(4)

BUGS

     This manual page is still confusing.